The only use I found for "Disguise Self" was changing the appearance of the ugly hirelings for aesthetic reasons... A lot of spells in the game just doesn't seem to have any real usefulness, even in areas where they should have
If you murder somebody and then cast speak with the dead on them to interrogate them they will often say that they are not willing to speak to their killer. Rarely, you can pass a persuasion check to talk to them anyway, but usually it fails. However, if you cast disguise self first then they will answer questions with gusto.
